Dissipation or re-direction of thermal energy is required by many electronic devices. For example, a computer contains several integrated circuits, e.g. CPU (central processing unit), GPU (graphics processing unit), Chipset (e.g. Northbridge/Southbridge), DRAM (dynamic random access memory), VRM (voltage regulator) etc. that generate heat. The GPU can be combined with the CPU on a computer motherboard as an APU (advanced processing unit) or the GPU can be included as part of a discrete graphics card. Further, many lighting applications use high-powered LED's (light emitting diodes) that generate heat. This heat needs to be removed to insure the reliability of the electronic device and to prevent premature failure.
The problem of heat dissipation is exacerbated by the increasing speed of electronic devices, e.g. overclocking of computer parts. Thus, there have been many attempts at heat dissipation for electronic devices. In the most basic case, the generated heat is allowed to simply dissipate by natural thermal convection. However, one disadvantage of natural thermal convection is that the heat transfer is relatively inefficient and consequently the temperature inside the electronic device rises fairly high before it reaches a steady temperature.
One cooling solution involves attaching a heat sink to an electronic device. The heat sink typically is made of materials like aluminum or copper and includes heat sink fins to maximize the heat exchanger-to-air surface area. To improve the thermal connection between the electronic device and the heat sink, a thermal interface material (TIM) is used. The TIM can, for example, consist of a colloidal silver paste.
Another cooling solution used in many computers includes a fan that directs forced air at the heat sink described above. As the thermal conductivity and heat capacity of air is smaller than the thermal conductivity and heat capacity of water, there have been methods proposed to cool electronic devices using water flow, similar to how a car engine is cooled. Such methods typically involve a pump, a coolant reservoir, a fan moving air over the radiator and a water/coolant block in thermal connection with the electronic device.
Yet a further alternative for cooling electronic devices consists of using a Peltier element. A Peltier element is a thermoelectric device that uses supplied electric current to cool down one side while the other side gets hot. The cold side of the Peltier element is mounted to the electronic device while a heat sink is attached to the hot side.
In addition, electronic device manufacturers have employed the use of heat pipes, also referred to as vapor chambers to re-direct heat from an electronic device to the ambient environment. A heat pipe is, for example, used on some motherboards and typically connects multiple electronic devices, e.g. southbridge and voltage regulators. In addition, a heat pipe can be incorporated in CPU/GPU cooling solutions and spreads heat from the CPU/GPU to a large area heat sink to which a fan is attached.
The heat pipe is made of copper or aluminum and consists of a sealed, hollow pipe, which is on the order of about ¼ inch (about 6 mm) in diameter. Inside the heat pipe is a wick on the inside wall of the pipe and a small amount of fluid which is in equilibrium with its own vapor. As the heat is applied to one side of the heat pipe, the working fluid vaporizes and the vapor spreads to the entire inner volume and condenses over a much larger surface. The condensate then returns to the evaporator via capillary forces developed in the wick.
However, all of the described heat dissipation techniques, firstly, require relatively large equipment for heat dissipation and, secondly, do not address the disadvantage of multiple thermal interfaces that hinder an effective heat transfer from an electronic device. For example a typical CPU thermal interface stack consists of a CPU, a first thermal interface material between the CPU and the lid, the lid, a second thermal interface material, a heat sink including a heat pipe and a fan.